Described herein is a reimageable display device capable of displaying color images. More particularly, described is a color display device having a novel stacked structure of an electrophoretic display portion or layer and a domain controlled liquid crystal display portion or layer.
The reimageable display devices herein are thus capable of generating images, including full color images, that do not exhibit the darkness issues associated with the use of color filter overlays. Moreover, the display device is able to utilize a relatively simple architecture to display different colors in an efficient manner, particularly as compared to electrophoretic displays utilizing three or more differently colored particles. The electrophoretic displays herein may be used for any display application, and particularly any display application where the image displayed may be changed, including, for example, reimageable paper, electronic books, electronic signage, watch, monitor (television and/or computer) and/or cell phone displays, and the like.
Electrophoretic displays are well known in the art. An electrophoretic display generally comprises a suspension of one or two charged pigment particles colloidally dispersed in a clear or colored liquid of matching specific gravity and contained in a cell comprising two parallel and transparent conducting electrode panels. The charged particles are transported between the electrode panels under the influence of an electric field, and can therefore be made to display an image through appropriate application of the electric field on the electrodes.
U.S. Pat. No. 6,113,810, incorporated herein by reference in its entirety, describes a dielectric dispersion for use in an electrophoretic display that includes a dielectric fluid, a first plurality of particles of a first color having a surface charge of a selected polarity dispersed within the dielectric fluid and a second plurality of particles of a second color having a surface charge of opposite polarity to that of the first plurality and a steric repulsion thereto preventing coagulation of the first and second plurality of particles.
U.S. Pat. Nos. 6,525,866 and 6,577,433, each incorporated herein by reference in its entirety, disclose an electrophoretic display liquid composition for use in an electrophoretic display device that has a multiplicity of individual reservoirs, each containing a display liquid comprised of two sets of particles dispersed in a transparent liquid system.
Electrophoretic display is thus based on the migration of charged particles suspended in an insulating fluid under the influence of an electric field. As discussed above, the display systems may comprise one-particle and two-particle systems. One-particle systems typically comprise one set of same color particles dispersed in a fluid that may have a color different from that of the particles. Two-particle systems typically comprise two sets of colored particles, with each set of particles having a different color dispersed in a fluid that is typically colorless/clear.
Another type of reimageable display is described in, for example, U.S. Pat. Nos. 6,858,266, incorporated herein by reference in its entirety. These systems comprise the use of domain controlled liquid crystals.
One approach for color devices involves the use of color filter overlays on black and white two-particle display systems, for example as in U.S. Pat. No. 6,850,355.
While known electrophoretic display devices, compositions and processes for displaying images are suitable for their intended purposes, a need remains for a color electrophoretic display with a simpler, cost effective design that efficiently achieves good color and good brightness.